what fried my power amp?

[walker rosewood]

I'll start by saying I'm not very well versed in power/electrical. I have a limited understanding of effects pedals circuit design, but not much beyond that. Also, I'm not the one who has to worry about fixing or replacing the amp, just curious why it happened and hope to prevent it in the future.

At the gig tonight we did the usual load in, set everything up, and I threw some tunes on from my iPod to eq the room. We were using different subs and a different amp rack then usual (but the same model of amps), but everything seemed normal. Turned the music off, but left the board (LS-9) and power amps on (Yorkville AP6040 for the subs, AP4040 for the mids, AP2020 for the highs, and a DBX260 driverack). Silent, for about 30 minutes while setting up backline and mics. Then some sudden popping, I turned quickly everything off, and smelled some fried parts, which quickly dissipated. It was the AP4040 that blew.

The other guy Mike, who does lights and power (he's an electrician) tested all our power with the multimeter and it was all running clean, 121v. We've been at this venue before without problems. There's no three phase, so we didn't use a distro or power tap, just running off the wall outlets. But Mike always checks the power and runs the lights, power, and peripherals off separate circuits.

We had a spare AP4040 in the rack which we used for the show, which went on without any further complications. So, what happened? My non-educated guess would be a power surge/voltage spike, but why did only the one amp take the hit? Or was the amp just ready to go? fwiw the Boss says he's never had any trouble with any yorkville amps before. Hopefully the amp's protection circuit did its job, and it's not an expensive fix.

If you made it threw this too lengthy post, thanks for reading. Thoughts?

[KeithAlanK]

Sometimes amps just die.
Has happened to me several times, and like you it was in venues I had worked many times with no trouble.

We recently got a brand new Mackie Onyx 24ch board, and at the very first gig the LEDs started flashing wildly and smoke came out of the vents. (Luckily I had our old board with me). We took it back to Sam Ash and as soon as the box was opened the guy could smell the stench of death and we got a new replacement right away, which has been flawless.

I have had Allen & Heath mixers go down with the power supply smoking, and these were less than a year old. I think they use really cheap bridge rectifiers.

If you think about all the little parts in a power amp--resistors and capacitors and transistors and such--that are made very fast in huge numbers for a couple pennies each, it's not hard to imagine one in a thousand failing, or more. Depending on where it is in the circuit, that one little failed part can take out a bunch of others with it, leaving you with an expensive repair.

When you get the diagnosis I'll bet it doesn't get you any closer to knowing why, and I wouldn't worry too much about it.

Gear fails, and it's usually nobody's fault. Just bad luck.

[mnphysicist]

As far as power disturbances go, its usually a cumulative thing. Ie, most single events (short of a nearby lightning hit) will not result in failure, and most test standards require a unit to handle a multitude of nasties before failure.

[D.A.R.K.]

that sounds like an amplifier component failure,
as opposed to spike/ electrical issue.

[walker rosewood]

You guys must be right, probably something in the amp that failed. All the amps in this rack have been used somewhat regularly for several years.